The present invention relates to a tire intended to be mounted on a rim having at least a first frustoconical seat, the generatrix of which has an axially outer end closer to the axis of rotation than the axially inner end.
Such a tire is described in international application WO 94/13498. It comprises at least a first bead, intended to be mounted on a first seat inclined towards the outside, the said first bead, having a seat the generatrix of which has its axially outer end closer to the axis of rotation than its axially inner end, and the said generatrix being extended axially towards to the outside by an outer face delimiting the bead toe, the said face forming with the axis of rotation an angle xcex3, open radially and axially towards the outside and of less than 90xc2x0. The radial carcass reinforcement of the said tire, anchored in each bead to at least an inextensible annular bead ring, has a meridian profile, when the tire is mounted on its service rim and inflated to its service pressure, with a constant direction of curvature in the sidewall and bead terminated by the toe and which is such that, in said bead, the tangent to the point of tangency of said profile with the inextensible bead ring forms with the axis of rotation an angle xc3x8 open towards the outside of at least 70xc2x0.
The bead of such a tire and more particularly the structure of the anchoring of carcass reinforcement may be variable. In the application WO 95/23073, the radial carcass reinforcement is anchored to the inextensible bead wire by winding around the said wire passing from the heel to the toe of the bead to form an upturn extending in a rubber section, made of rubber mix in the form of a wedge defined by two sides coming from an apex A located beneath the meridian section of the coated bead wire, the radially outer side forming, with a line parallel to the axis of rotation passing through said apex A, an acute angle xc3x81, open radially towards the outside and between 20xc2x0 and 70xc2x0, and the radially inner side forming with said parallel line an acute angle xc3x82, open radially towards the inside, the rubber mix forming the rubber section axially adjacent to the bead wire having a Shore A hardness greater than the Shore A hardness(es) of the rubber mixes located axially and radially above the wire and the rubber section.
The combination of the carcass reinforcement meridian profile such as described in the first cited application with a structure of hooking such as described in the second cited application makes possible to obtain a very good compromise between the handling properties of the tire inflated to its recommended pressure and the said properties when the tire is inflated to a reduced pressure or even zero. Whether the initial clamping on the rim be zero or of a given value, the axial displacement of the anchoring bead wire of the carcass reinforcement, which may result from the tension of said reinforcement, which tension is due, for instance, to the inflation pressure of the tire, makes possible, in combination with the axial disposition of the rubber section reinforced by the upturn, to obtain clamping of the toe of the bead on the rim seat. The value of this clamping increases as a function of the tension force to which the carcass reinforcement is subjected, and may become great in the case of high tension, for instance when one of the side walls of the tire is placed under great tension by a transverse force.
The preferential solution described in the application WO 95/23073 is such that the carcass reinforcement upturn has a length such that it is in contact with the total perimeter of the rubber section or wedge; it thus forms the two radially outer and inner sides of the rubber section and the side opposite the apex or center of said rubber section, and its end is located axially beyond the point of intersection of the two outer and inner sides. The part of the upturn immediately adjacent to the part of said upturn which is wound around the bead wire may, in the first instance, form the radially outer edge of the rubber section or wedge and then finally the radially inner side of said rubber section, ending beyond the junction point of the two outer and inner sides. It may also form firstly the radially inner side of the rubber section or wedge, then the side opposite the apex of said wedge, and then finally the radially outer side of said rubber section, ending in the same manner as previously described.
The above two structures are complicated and difficult to use industrially, and as a consequence, expensive. Furthermore, in severe conditions of load, the contact pressure exerted by the bead toe upon the axially outer hump of the rim and the great temperature that may be reached in the said bead are such that fissures of rubber may occur in the external protecting layer of the bead, fissures which are propagated along the upturn of the carcass reinforcement and reach the radially inner face of the anchoring bead wire with destruction of the bead.
The invention has for object to remedy these drawbacks while keeping the excellent properties of unseating of tire beads.
According to the invention, a tire with a radial carcass reinforcement, when viewed in meridian section, comprises at least a first bead, the seat of which has a generatrix the axially inner end of which is on a circle of a diameter greater than the diameter of a circle on which is the axially outer end, the heel of the bead being axially on the inside and being reinforced by at least a reinforcement ring, annular, inextensible and coated with a rubber mix, the toe of bead being axially on the outside and comprising a rubber section made of rubber mix in the form of a wedge delimited by two sides coming from an apex A located beneath the meridian section of the coated bead ring, the radially outer side forming, with a line parallel to the axis of rotation passing through said apex A, an acute angle xc3x81, open radially and axially towards the outside, and the radially inner side forming with said parallel line an acute angle xc3x82, open radially towards the inside, the rubber mix forming the rubber section axially adjacent to the bead ring, having a Shore A hardness greater than the Shore A hardness(es) of the rubber mixes located axially and radially above the bead ring and above the rubber section, is characterized in that the carcass reinforcement of the said tire is wound, at least in the first bead, around the bead ring passing from the inside to the outside to form an upturn extending along the radially inner side of the rubber section in form of a wedge, then along the side opposite the apex A, and then covers axially and radially on the outside, at least in part, the rubber section radially above the rubber section or wedge, the said upturn having an end located radially above the reinforcement annular ring of bead and axially between the straight line, extending the radially outer side of the wedge, and the straight line perpendicular to the axis of rotation and tangent at N to the said annular ring.
Preferably, the tire comprises a second bead, the seat of which has the same configuration as the seat of the first bead, i.e a seat the generatrix of which has an axially inner end on a circle of diameter greater than the diameter of the circle on which is the axially outer end or seat inclined towards the outside.
The invention also provides a tire which, when viewed in meridian section, has a radial carcass reinforcement and a bead of specified structure. The bead comprises a reinforcement ring that is able to move axially. The tire further comprises means in each bead permitting modification of clamping of the bead on a rim as a function of the tension of the carcass reinforcement. In one embodiment, the tire comprises, viewed in meridian section, a radial carcass reinforcement and a bead having a reinforcement ring, the reinforcement ring being able to be moved axially, and means responsive to the axial movement of the reinforcement ring for modifying clamping of the bead on its rim, so that the clamping is increased with increasing tension of the carcass reinforcement.
If the diameter of a seat is the diameter of the circle on which is the end of its generatrix farthest from the axis of rotation, the tire has preferably two seats inclined towards the outside and the two seats have unequal diameters.
The meridian profile of the carcass reinforcement, when the tire is mounted on its service rim and inflated to its service pressure, has a constant direction of curvature, at least in the first bead and the sidewall which extends it, and the tangent TTxe2x80x2 to the point of tangency T of said profile with the reinforcement of the said bead forms with the axis of rotation an angle xc3x8 open towards the outside at least equal to 70xc2x0.